The influence of probe level on the tuning of stimulus frequency otoacoustic emissions and behavioral test in human.

Wang Y, Gong Q, Zhang T - Biomed Eng Online (2016)

Bottom Line:
Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds.The study included 15 young subjects with normal hearing.Because SFOAE STCs are not biased by higher levels auditory processing, they may represent cochlear FS better than PTCs.

Background: Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds. Although direct measurements of cochlear FS require surgical preparation, it can also be estimated with the measurements of otoacoustic emissions or behavioral tests, including stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs) or psychophysical tuning curves (PTCs). These two methods result in similar estimates of FS at low probe levels. As the compressive nonlinearity of cochlea is strongly dependent on the stimulus intensity, the sharpness of tuning curves which is relevant to the cochlear nonlinearity will change as a function of probe level. The present study aims to investigate the influence of different probe levels on the relationship between SFOAE STCs and PTCs.

Methods: The study included 15 young subjects with normal hearing. SFOAE STCs and PTCs were recorded at low and moderate probe levels for frequencies centred at 1, 2, and 4 kHz. The ratio or the difference of the characteristic parameters between the two methods was calculated at each probe level. The effect of probe level on the ratio or the difference between the parameters of SFOAE STCs and PTCs was then statistically analysed.

Results: The tuning of SFOAE STCs was significantly positively correlated with the tuning of the PTCs at both low and moderate probe levels; yet, at the moderate probe level, the SFOAE STCs were consistently broader than the PTCs. The mean ratio of sharpness of tuning at low probe levels was constantly around 1 while around 1.5 at moderate probe levels.

Conclusions: Probe level had a significant effect on the sharpness of tuning between the two methods of estimating FS. SFOAE STC seems a good alternative measurement of PTC for FS assessment at low probe levels. At moderate probe levels, SFOAE STC and PTC were not equivalent measures of the FS in terms of their bandwidths. Because SFOAE STCs are not biased by higher levels auditory processing, they may represent cochlear FS better than PTCs.

Mentions:
In order to compare the difference between the ftip shift of SFOAE STCs and PTCs at different probe levels, the ftip shift difference using the absolute value for each subject is calculated as the ftip shift of PTCs minus SFOAE STCs’. Mean values of frequency shift and frequency shift difference at the tip for SFOAE STCs and PTCs at both low and moderate probe levels as a function of fp are illustrated in Fig. 5a and b respectively. The SFOAE STCs shift was higher at the moderate Lp than that at lower Lp except for 2 kHz, while the tips of PTCs always coincided with fp independent of fp and Lp (Fig. 5a). The mean ftip shift difference at the moderate Lp was larger than that at low Lp (Fig. 5b). Two-factor Scheirer-Ray-Hare test revealed that neither Lp nor fp had a significant effect on the frequency shift differences (absolute value) between SFOAE STCs and PTCs (Lp: df = 1, H = 3.0495, P = .0808; fp: df = 2, H = .3401, P = .8436), and no interactions were found between the factors of level and frequency (df = 2, H = 1.4371, P = .4875).Fig. 5

Mentions:
In order to compare the difference between the ftip shift of SFOAE STCs and PTCs at different probe levels, the ftip shift difference using the absolute value for each subject is calculated as the ftip shift of PTCs minus SFOAE STCs’. Mean values of frequency shift and frequency shift difference at the tip for SFOAE STCs and PTCs at both low and moderate probe levels as a function of fp are illustrated in Fig. 5a and b respectively. The SFOAE STCs shift was higher at the moderate Lp than that at lower Lp except for 2 kHz, while the tips of PTCs always coincided with fp independent of fp and Lp (Fig. 5a). The mean ftip shift difference at the moderate Lp was larger than that at low Lp (Fig. 5b). Two-factor Scheirer-Ray-Hare test revealed that neither Lp nor fp had a significant effect on the frequency shift differences (absolute value) between SFOAE STCs and PTCs (Lp: df = 1, H = 3.0495, P = .0808; fp: df = 2, H = .3401, P = .8436), and no interactions were found between the factors of level and frequency (df = 2, H = 1.4371, P = .4875).Fig. 5

Bottom Line:
Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds.The study included 15 young subjects with normal hearing.Because SFOAE STCs are not biased by higher levels auditory processing, they may represent cochlear FS better than PTCs.

Background: Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds. Although direct measurements of cochlear FS require surgical preparation, it can also be estimated with the measurements of otoacoustic emissions or behavioral tests, including stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs) or psychophysical tuning curves (PTCs). These two methods result in similar estimates of FS at low probe levels. As the compressive nonlinearity of cochlea is strongly dependent on the stimulus intensity, the sharpness of tuning curves which is relevant to the cochlear nonlinearity will change as a function of probe level. The present study aims to investigate the influence of different probe levels on the relationship between SFOAE STCs and PTCs.

Methods: The study included 15 young subjects with normal hearing. SFOAE STCs and PTCs were recorded at low and moderate probe levels for frequencies centred at 1, 2, and 4 kHz. The ratio or the difference of the characteristic parameters between the two methods was calculated at each probe level. The effect of probe level on the ratio or the difference between the parameters of SFOAE STCs and PTCs was then statistically analysed.

Results: The tuning of SFOAE STCs was significantly positively correlated with the tuning of the PTCs at both low and moderate probe levels; yet, at the moderate probe level, the SFOAE STCs were consistently broader than the PTCs. The mean ratio of sharpness of tuning at low probe levels was constantly around 1 while around 1.5 at moderate probe levels.

Conclusions: Probe level had a significant effect on the sharpness of tuning between the two methods of estimating FS. SFOAE STC seems a good alternative measurement of PTC for FS assessment at low probe levels. At moderate probe levels, SFOAE STC and PTC were not equivalent measures of the FS in terms of their bandwidths. Because SFOAE STCs are not biased by higher levels auditory processing, they may represent cochlear FS better than PTCs.